Fiber-reinforced ceramic composites are materials which have many utilities and are used, e.g., for aeronautical applications, radomes, draw rollers for synthetic filaments, and tools. Fibers which have been utilized in the preparation of the composites include carbon fibers, sized carbon fibers, and silicon carbide fibers; and polysilazane compositions, such as those of U.S. Pat. No. 4,482,669 (Seyferth et al.-I), have been taught to be useful in preparing the ceramic matrices.
When producing a fiber-reinforced ceramic composite, it is convenient to coat loose or woven fibers with a solution or dispersion of a preceramic material, dry the coating to bond the fibers together with a matrix and form a prepreg, laminate layers of the prepreg, and heat the resultant laminate to pyrolyze the matrix. The porous composite thus formed can then be infiltrated with a preceramic composition, if desired, and subjected to pyrolysis to form a denser composite having increased strength.
Copending applications S N. (Case CE-6102-B) (Yu et al.) and S. N. (Case CE-6294) (Liimatta et al.) teach crosslinkable preceramic polysilazane/unsaturated compound blends which are useful as infiltrants for fiber-reinforced ceramic composites, as well as dispersions of ceramic powders in such blends which can be employed in forming the matrices. In Yu et al. the polysilazane is a mixture of low and medium molecular weight polysilazanes, while the polysilazane of Liimatta et al. is a low molecular weight polysilazane; and the unsaturated component of each of the compositions is an organic or organosilicon compound containing at least two alkenyl groups.
U.S. Pat. Nos. 4,904,818 (Minami et al.) and 4,923,752 (Cornelia) disclose the utility of a bisphenol/polyalkylene etherester copolymer and a fluorinated poly(amide-acid), respectively, as sizing agents which improve the handleability of carbon fibers used in preparing carbon fiber-reinforced plastics. Copending application Ser. No. 07/301,451 (Niebylski-I) teaches that a trialkoxy-, triaryloxy-, or tri(arylalkoxy)boroxine, preferably in conjunction with a strong acid, can be used to size carbon fibers and protect them from mechanical damage and oxidative deterioration in the preparation and use of fiber-reinforced composites.
Copending application Ser. No. 07/446,184 (Niebylski-II) discloses coating compositions which are especially valuable in forming buffer layers in multilayer ceramic coatings and which comprise mixtures of Group IIIB and IVA metal hydrocarbyloxides; a bis-, tris-, or tetrakis(dialkylamino)metal of Group IVA; a polysilazane and/or a bis-, tris-, or tetrakis(dialkylamino)silane; and optional cyclopentadienyl Group IVA metal halide.
The teachings of copending application Ser. No. 07/466,622 (Niebylski-III) relate to compositions which are particularly useful for coating normally oxidizable substrates and which comprise dispersions of silicon metal, silicon boride, and optional aluminum-silicon eutectic and/or silicon carbide in polysilazane solutions.